Methods and systems for advanced harmonic energy

ABSTRACT

Aspects of the present disclosure are presented for a medical instrument configured to adjust the power level for sealing procedures to account for changes in tissue impedance levels over time. In some aspects, a medical instrument may be configured to apply power according to a power algorithm to seal tissue by applying a gradually lower amount of power over time as the tissue impedance level begins to rise out of the “bathtub region,” which is the time period during energy application where the tissue impedance is low enough for electrosurgical energy to be effective for sealing tissue. In some aspects, the power is then cut once the tissue impedance level exceeds the “bathtub region.” By gradually reducing the power, a balance is achieved between still applying an effective level of power for sealing and prolonging the time in which the tissue impedance remains in the “bathtub region.”

TECHNICAL FIELD

The present disclosure is related generally to medical devices withvarious mechanisms for grasping and sealing tissue. In particular, thepresent disclosure is related to electrosurgical instruments configuredto regulate the application of energy applied to a surgical site toprolong the sealing time duration when performing sealing procedures.

BACKGROUND

Electrosurgical instruments are a type of surgical instrument used inmany surgical operations. Electrosurgical instruments apply electricalenergy to tissue in order to treat tissue. An electrosurgical instrumentmay comprise an instrument having a distally-mounted end effectorcomprising one or more electrodes. The end effector can be positionedagainst tissue such that electrical current is introduced into thetissue. Electrosurgical instruments can be configured for bipolar ormonopolar operation. During bipolar operation, current is introducedinto and returned from the tissue by active and return electrodes,respectively, of the end effector. During monopolar operation, currentis introduced into the tissue by an active (or source) electrode of theend effector and returned through a return electrode (e.g., a groundingpad) separately located on a patient's body. Heat generated by thecurrent flow through the tissue may form hemostatic seals within thetissue and/or between tissues and thus may be particularly useful forsealing blood vessels, for example. The end effector of anelectrosurgical instrument sometimes also comprises a cutting memberthat is moveable relative to the tissue and the electrodes to transectthe tissue.

Energy applied by an electrosurgical instrument can be transmitted tothe instrument by a generator. The generator may form an electrosurgicalsignal that is applied to an electrode or electrodes of theelectrosurgical instrument. The generator may be external or integral tothe electrosurgical instrument. The electrosurgical signal may be in theform of radio frequency (“RF”) energy. For example, RF energy may beprovided at a frequency range of between 100 kHz and 1 MHz. Duringoperation, an electrosurgical instrument can transmit RF energy throughtissue, which causes ionic agitation, or friction, in effect resistiveheating, thereby increasing the temperature of the tissue. Because asharp boundary may be created between the affected tissue and thesurrounding tissue, surgeons can operate with a high level of precisionand control, without sacrificing un-targeted adjacent tissue. The lowoperating temperatures of RF energy may be useful for removing,shrinking, or sculpting soft tissue while simultaneously sealing bloodvessels. RF energy may work particularly well on connective tissue,which is primarily comprised of collagen and shrinks when contacted byheat. In some cases, the instrument may also be configured to applyultrasonic energy to create homeostasis. The generator may be configuredto transmit energy which is converted into ultrasonic vibrations at theend effector. The energy transmitted to the tissue may similarly causeresistive heating through the ultrasonic vibrations.

During the application of the energy to tissue, the impedance of thetissue indicates the condition of the tissue. After a certain amount ofenergy applied, the impedance of the tissue dramatically increases andreduces the effectiveness of the further energy applied in the sealingprocedure. Furthermore, as the tissue impedance approaches thisthreshold level where further energy applied is no longer effective,certain chemical processes in the tissue occur that would be desirableto be controlled better. The period of time under which the tissueresponds to the sealing energy is sometimes referred to as the “bathtubregion,” based on the shape of the level of impedance over time at whichthe tissue effectively responds to the sealing energy. There is a needtherefore to better control the rise of impedance levels in the tissueand to prolong the period under which the tissue still responds (e.g.,prolong the “bathtub region”) to applied energy during sealingprocedures. While several devices have been made and used, it isbelieved that no one prior to the inventors has made or used the devicedescribed in the appended claims.

SUMMARY

In some aspects, a surgical system is provided.

In one aspect, the surgical system may include: an end effectorcomprising at least one energy delivery component configured to transmitelectrosurgical energy at a number of different power levels (i.e.,rates of energy delivery or levels of energy delivery) to tissue at asurgical site; and a control circuit communicatively coupled to theenergy delivery component and programmed to: for a first applicationperiod, cause the energy delivery component to transmit theelectrosurgical energy at a first power level or rate of energydelivery, the first application period comprising a point in time whereimpedance of the tissue reaches a minimum value; for a secondapplication period after the first application period, cause the energydelivery component to transmit the electrosurgical energy at adecreasing power level or rate of energy level from the first powerlevel until a second power level is reached, the second power levellower than the first power level and the second application periodcomprising a point in time where the impedance of the tissue rises abovethe minimum impedance value; for a third application period after thesecond application period, cause the energy delivery component totransmit the electrosurgical energy at a third power level, the thirdpower level lower than the second power level and the third applicationperiod comprising a point in time where the impedance of the tissuerises above a transition impedance threshold level.

In another aspect of the surgical system, the first application periodand the second application period combined comprise a time period wherethe electrosurgical energy causes sealing of the tissue at the surgicalsite.

In another aspect of the surgical system, the third application periodfurther comprises a time period where the impedance of the tissue risesto a level such that the electrosurgical energy no longer causes sealingof the tissue at the surgical site.

In another aspect, the surgical system further comprises at least onesensor configured to measure an initial level of impedance in the tissueand a minimum level of impedance in the tissue.

In another aspect of the surgical system, the control circuit is furtherprogrammed to determine a beginning of the third application periodbased on the measured initial level of impedance in the tissue.

In another aspect of the surgical system, the control circuit is furtherprogrammed to determine a beginning of the third application periodbased on the measured minimum level of impedance in the tissue.

In another aspect of the surgical system, the first application periodand the second application period combined comprise a continuous timeperiod where the tissue impedance remains below an initial level ofimpedance in the tissue.

In another aspect of the surgical system, the energy delivery componentis configured to transmit RF and ultrasonic energy.

In other aspects, a method for transmitting electrosurgical energy totissue at a surgical site by a surgical system is provided. The methodmay include: causing, by an energy delivery component of a surgicalsystem, electrosurgical energy to be applied to the tissue; measuring,by at least one sensor of the surgical system, a benchmark level ofimpedance of the tissue; determining, among a plurality of power loadcurve algorithms, a power load curve algorithm to be applied to theenergy delivery component, based on the measured benchmark level ofimpedance of the tissue; based on the determined power load curvealgorithm: for a first application period, causing the energy deliverycomponent to transmit the electrosurgical energy at a first power level,the first application period comprising a point in time where impedanceof the tissue reaches a minimum value; for a second application periodafter the first application period, cause the energy delivery componentto transmit the electrosurgical energy at a decreasing power level fromthe first power level until a second power level is reached, the secondpower level lower than the first power level and the second applicationperiod comprising a point in time where the impedance of the tissuerises above the minimum impedance value; for a third application periodafter the second application period, cause the energy delivery componentto transmit the electrosurgical energy at a third power level, the thirdpower level lower than the second power level and the third applicationperiod comprising a point in time where the impedance of the tissuerises above a transition impedance threshold level.

In other aspects of the method, determining the power load curvealgorithm comprises determining whether the benchmark level of impedanceis less than a first threshold impedance value, whether the benchmarklevel of impedance is greater than the first threshold impedance valueand less than a second threshold impedance value, and whether thebenchmark level of impedance is greater than the second thresholdimpedance value.

In other aspects of the method, the first application period and thesecond application period combined comprise a time period where theelectrosurgical energy is delivered at a higher rate and causes sealingof the tissue at the surgical site.

In other aspects of the method, the third application period furthercomprises a time period where the impedance of the tissue rises to alevel such that the electrosurgical energy is delivered at a lower rateand no longer causes sealing of the tissue at the surgical site.

In other aspects of the method, the benchmark level of impedance is theminimum impedance value or an initial level of impedance of the tissue.

In other aspects of the method, a beginning of the third applicationperiod is based on the measured benchmark level of impedance.

In other aspects of the method, the first application period and thesecond application period combined comprise a continuous time periodwhere the tissue impedance remains below an initial level of impedancein the tissue.

In other aspects of the method, the energy delivery component isconfigured to transmit RF and ultrasonic energy.

In other aspects, a surgical instrument is provided. The surgicalinstrument may include: a handle assembly; a shaft coupled to a distalend of the handle assembly; an end effector coupled to a distal end ofthe shaft and comprising at least one energy delivery componentconfigured to transmit electrosurgical energy to tissue at a surgicalsite; and a control circuit communicatively coupled to the energydelivery component and programmed to: for a first application period,cause the energy delivery component to transmit the electrosurgicalenergy at a first energy level, the first application period comprisinga point in time where impedance of the tissue reaches a minimum value;for a second application period after the first application period,cause the energy delivery component to transmit the electrosurgicalenergy at a decreasing energy level from the first energy level until asecond energy level is reached, the second energy level lower than thefirst energy level and the second application period comprising a pointin time where the impedance of the tissue rises above the minimumimpedance value; for a third application period after the secondapplication period, cause the energy delivery component to transmit theelectrosurgical energy at a third energy level, the third energy levellower than the second energy level and the third application periodcomprising a point in time where the impedance of the tissue rises abovea transition impedance threshold level.

In another aspect of the surgical instrument, the first applicationperiod and the second application period combined comprise a time periodwhere the electrosurgical energy causes sealing of the tissue at thesurgical site.

In another aspect of the surgical instrument, the third applicationperiod further comprises a time period where the impedance of the tissuerises to a level such that the electrosurgical energy no longer causessealing of the tissue at the surgical site.

In another aspect, the surgical instrument further comprises at leastone sensor configured to measure an initial level of impedance in thetissue and a minimum level of impedance in the tissue.

In other aspects, a non-transitory computer readable medium ispresented. The computer readable medium may include instructions that,when executed by a processor, cause the processor to perform operationscomprising any of the operations described in any one of the previousaspects.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects and featuresdescribed above, further aspects and features will become apparent byreference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the aspects described herein are set forth withparticularity in the appended claims. The aspects, however, both as toorganization and methods of operation may be better understood byreference to the following description, taken in conjunction with theaccompanying drawings as follows.

FIG. 1A shows one example of a surgical instrument system, according tosome aspects.

FIG. 1B shows another example of a surgical instrument system, in thiscase showing multiple versions of a surgical instrument configured todeliver RF energy, ultrasonic energy, or a combination of both,according to some aspects.

FIG. 1C is a side, partially transparent schematic view of one aspect ofa powered surgical device.

FIG. 1D is a side, partially transparent schematic view of anotheraspect of a powered surgical device.

FIG. 2 shows a perspective view of an end effector with jaws open,according to some aspects.

FIG. 3 is a block diagram describing further details of power supplyelements of a surgical system, the surgical instrument coupled to agenerator, according to some aspects.

FIG. 4A provides a visual depiction of the level of impedance over timepresent in tissue undergoing a sealing procedure during surgery.

FIG. 4B provides further details of various electrical readings of thesurgical instrument system undergoing the sealing procedure duringsurgery.

FIG. 5 provides another example of the level of tissue impedance overtime, this time using more empirical data.

FIG. 6A illustrates an example power profile of an amount ofelectrosurgical energy applied by a surgical instrument to tissue at asurgical site over time, in order to extend or prolong the bathtubregion, according to some aspects.

FIG. 6B shows an example adjusted impedance profile over time as aresult of the adjusted power applied to the surgical instrument, such asthe example power profile in FIG. 6A, according to some aspects.

FIG. 7 shows an example power profile of the tapered load curve conceptintroduced in FIG. 6A, with additional power characteristicssuperimposed.

FIG. 8 provides an example of how multiple load curves may be programmedinto the surgical instrument to apply different power adjustments basedon impedance measurements during the sealing procedures.

FIG. 9 shows a visual depiction of an example load curve under the lowminimum impedance threshold (see FIG. 8), according to some aspects.

FIG. 10 shows a visual depiction of an example load curve under themedium minimum impedance threshold (see FIG. 8), according to someaspects.

FIG. 11 is a graphical representation of impedance threshold and minimumpulse duration showing an example of additional adjustments that can bemade to varying the power to account for other tissue properties.

FIG. 12 is a graphical illustration of voltage cutback caused by animpedance threshold greater than 325 Ohms, according to one aspect ofthe present invention.

FIG. 13 is a graphical illustration of a power pulse region of thegraphical illustration shown in FIG. 11, according to one aspect of thepresent disclosure.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings,similar symbols and reference characters typically identify similarcomponents throughout the several views, unless context dictatesotherwise. The illustrative aspects described in the detaileddescription, drawings, and claims are not meant to be limiting. Otheraspects may be utilized, and other changes may be made, withoutdeparting from the scope of the subject matter presented here.

The following description of certain examples of the technology shouldnot be used to limit its scope. Other examples, features, aspects,aspects, and advantages of the technology will become apparent to thoseskilled in the art from the following description, which is, by way ofillustration, one of the best modes contemplated for carrying out thetechnology. As will be realized, the technology described herein iscapable of other different and obvious aspects, all without departingfrom the technology. Accordingly, the drawings and descriptions shouldbe regarded as illustrative in nature and not restrictive.

It is further understood that any one or more of the teachings,expressions, aspects, examples, etc. described herein may be combinedwith any one or more of the other teachings, expressions, aspects,examples, etc. that are described herein. The following describedteachings, expressions, aspects, examples, etc. should, therefore, notbe viewed in isolation relative to each other. Various suitable ways inwhich the teachings herein may be combined will be readily apparent tothose of ordinary skill in the art in view of the teachings herein. Suchmodifications and variations are intended to be included within thescope of the claims.

Also, in the following description, it is to be understood that termssuch as front, back, inside, outside, upper, lower, and the like arewords of convenience and are not to be construed as limiting terms.Terminology used herein is not meant to be limiting insofar as devicesdescribed herein, or portions thereof, may be attached or utilized inother orientations. The various aspects will be described in more detailwith reference to the drawings. Throughout this disclosure, the term“proximal” is used to describe the side of a component, e.g., a shaft, ahandle assembly, etc., closer to a user operating the surgicalinstrument, e.g., a surgeon, and the term “distal” is used to describethe side of the component farther from the user operating the surgicalinstrument.

Aspects of the present disclosure are presented for a medical instrumentconfigured to adjust the power level for sealing procedures to accountfor changes in tissue impedance levels over time. Typically duringsealing procedures, a period of time exists where the tissue impedancelevel is low enough to allow for the tissue to respond to energy appliedto it. The impedance level typically dips slightly over time initially,and then rises. After a certain point, due to various heating andchemical factors, the level of impedance rises dramatically, and energyapplied to the tissue is no longer effective. Further example details ofthe limits of any power sources over a range of loads are described insome of the accompanying figures, below. The period of time where thelevel of impedance is low enough for applied energy to be effective issometimes referred to as the “bathtub” region, due to the initial dip inthe level of impedance and subsequent slow rise. It is desirable tomanipulate the level of power applied to the tissue in order to extendor prolong the length of this bathtub region, so that the period of timefor sealing and manipulating the tissue may be extended.

In some aspects, a medical instrument may be configured to apply poweraccording to a power algorithm to seal tissue by applying a graduallylower amount of power over to time as the tissue impedance level beginsto rise out of the “bathtub region.” In some aspects, the power is thencut once the tissue impedance level exceeds the “bathtub region.” Bygradually reducing the power, a balance is achieved between stillapplying an effective level of power for sealing and prolonging the timein which the tissue impedance remains in the “bathtub region,” due tothe reduced power.

The medical instrument of the present disclosures may include additionalfeatures. An end effector of the electrosurgical device may includemultiple members arranged in various configurations to collectivelyperform the aforementioned functions. As used herein, an end effectormay be referred to as a jaw assembly or clamp jaw assembly comprising anupper jaw member and a lower jaw member where at least one of the upperjaw member and the lower jaw member may be movable relative to theother. Each of the jaw members may be adapted to connect to anelectrosurgical energy source. Each jaw member may incorporate anelectrode. The electrode may be a positive or negative electrode. In abipolar electrosurgical device, the electrodes may be adapted forconnection to the opposite terminals of the electrosurgical energysource, such as a bipolar radio frequency (RF) generator, so as togenerate a current flow therebetween. An electrosurgical energy may beselectively communicated through tissue held between the jaw members toeffect a tissue seal and/or treatment. Tissue may be coagulated from thecurrent flowing between the opposite polarity electrodes on each jawmember.

At least one jaw member may include a knife channel defined thereinconfigured to reciprocate a knife there along for severing tissue heldbetween the jaw members. The knife channel may be an extended slot inthe jaw member. The knife may be provided within a recess associatedwith the at least one jaw member. The electrosurgical device may haveboth coagulation and cutting functions. This may eliminate or reduceinstrument interchange during a surgery. Cutting may be achieved usingmechanical force alone or a combination of mechanical force and theelectrosurgical energy. The electrosurgical energy may be selectivelyused for coagulation and/or cutting. The knife may be made from anelectrically conductive material adapted to connect to theelectrosurgical source, and selectively activatable to separate tissuedisposed between the jaw members. The knife may be spring biased suchthat once tissue is severed, the knife may automatically return to anunengaged position within the knife channel or a retracted position inthe recess.

In some aspects, the jaw members may be movable relative to each other.During operation of the electrosurgical device, at least one of the jawmembers may move from a first, open position where the jaw members canbe disposed around a mass of tissue, to a second, closed position wherethe jaw members grasp the tissue. The jaw members therefore may movethrough a graspers-like range of motion, similar to that of conventionalpliers. In the second position, current flows between the jaw members toachieve hemostasis of the tissue captured therebetween. The jaw membersmay be configured to have a relatively thick proximal portion to resistbending. At least one of the jaw members may have a three-dimensionalconfiguration with a D-shaped cross-sectional. The three-dimensionalconfiguration with the D-shaped cross-sectional may resist bending. Alock mechanism may be included to lock the jaw members in the closedposition. The lock mechanism may set the clamp pressure between the jawmembers. At least one electrically conductive gap setting member may beprovided between the jaw members to establish a desired gap betweenelectrodes in bipolar electrosurgical devices.

The electrosurgical device may incorporate components to grasp a tissuevia the end effector, deliver energy to the tissue via one or moreelectrodes, and cut the tissue via a dissecting device such as a tissueknife. The structural capabilities of any aspect of an electrosurgicaldevice may be designed for use in one or more of a variety of surgicalprocedures. In some surgical procedures, the treated tissue may bereadily accessible to an end effector affixed to a relatively straightand unbendable shaft. In some alternative surgical procedures, thetissue may not be readily accessible to the end effector on such ashaft. In such procedures, the electrosurgical device may incorporate ashaft designed to bend so that the end effector may contact the tissuerequiring treatment. In such a device, the shaft may include one or morearticulated joints that may permit the shaft to bend under control bythe user. A sliding knife may include a feature to provide actuatingforce to the sliding knife. A knife actuator may be operably coupled tothe shaft for selectively reciprocating the knife through the knifechannel.

A front portion assembly may be designed for a specific surgicalprocedure, while a reusable handle assembly, configured to releasablyattach to a front portion assembly, may be designed to provide controlof surgical functions common to each front portion assembly, such astissue grasping, cauterizing, and cutting. Consequently, the number andtypes of devices required for surgeries can be reduced. The reusablehandle assembly may be designed to automate common functions of theelectrosurgical device. Device intelligence may be provided by acontroller located in the reusable handle assembly that is configured toreceive information from a front portion assembly. Such information mayinclude data regarding the type and use of the front portion assembly.Alternatively, information may include data indicative of the positionand/or activation of control components (such as buttons or slides thatcan be manipulated) that may indicate what system functions should beactivated and in what manner.

In some non-limiting examples, the controller may supply the RF currentwhen the energy activation control is placed in an activating positionby the user. In some alternative non-limiting examples, the controllermay supply the RF current for a predetermined period of time once theenergy activation control is placed in an activating position. In yetanother non-limiting example, the controller may receive data related tothe position of the jaws and prevent the RF current from being suppliedto the one or more tissue cauterization power contacts if the jaws arenot in a closed position.

In some aspects, any of the mentioned examples also may be configured toarticulate along at least one axis through various means, including, forexample, a series of joints, one or more hinges or flexure bearings, andone or more cam or pulley systems. Other features may include cameras orlights coupled to one or more of the members of the end effector, andvarious energy options for the surgical device.

The electrosurgical device can be configured to source energy in variousforms including, without limitation, electrical energy, monopolar and/orbipolar RF energy, microwave energy, reversible and/or irreversibleelectroporation energy, and/or ultrasonic energy, heat energy, or anycombination thereof, to the tissue of a patient either independently orsimultaneously. The energy can be transmitted to the electrosurgicaldevice by a power source in electrical communication with theelectrosurgical device. The power source may be a generator. The powersource may be connected to the electrosurgical device via a suitabletransmission medium such as a cable. The power source may be separatefrom the electrosurgical device or may be formed integrally with theelectrosurgical device to form a unitary electrosurgical system. In onenon-limiting example, the power source may include one or more batterieslocated within a portion of the electrosurgical device. It may beunderstood that the power source may source energy for use on the tissueof the patient as well as for any other electrical use by other devices,including, without limitation, lights, sensors, communication systems,indicators, and displays, which operate in relation to and/or with theelectrosurgical device to form an electrosurgical system. In someaspects, the power source may source energy for use in measuring tissueeffects with an RF impedance measuring portion. The remaining sources ofenergy, such as ultrasonic energy, may then be controlled based on themeasured tissue effects. Similarly, multiple types of energy from one ormore sources may be combined to interact in distinct ways. For example,an instrument with both RF and ultrasonic capabilities may allow fordifferent energy types to perform different functions during a singleprocedure. For example, RF energy may be used to seal, while otherenergy types, such as ultrasonic energy, may be used to cut the tissue.In general, the present disclosures may be applied to these devices withcombination elements (e.g., instruments having both RF and ultrasonicenergy functionalities), and aspects are not so limited. Similarconcepts include the systems and methods described in U.S. Pat. No.9,017,326, “IMPEDANCE MONITORING APPARATUS, SYSTEM, AND METHOD FORULTRASONIC SURGICAL INSTRUMENTS,” which is incorporated herein byreference.

The electrosurgical device may be configured to source electrical energyin the form of RF energy. The electrosurgical device can transmit the RFenergy through tissue compressed between two or more jaws. Such RFenergy may cause ionic agitation in the tissue, in effect producingresistive heating, and thereby increasing the temperature of the tissue.Increased temperature of the tissue may lead to tissue cauterization. Insome surgical procedures, RF energy may be useful for removing,shrinking, or sculpting soft tissue while simultaneously sealing bloodvessels. RF energy may work particularly well on connective tissue,which is primarily composed of collagen and shrinks when contacted byheat. Because a sharp boundary may be created between the affectedtissue and the surrounding tissue, surgeons can operate with a highlevel of precision and control, without sacrificing untargeted adjacenttissue.

The RF energy may be in a frequency range described in EN60601-2-2:2009+A11:2011, Definition 201.3.218—HIGH FREQUENCY. Forexample, the frequency in monopolar RF applications may be typicallyrestricted to less than 5 MHz. However, in bipolar RF applications, thefrequency can be almost anything. Frequencies above 200 kHz can betypically used for monopolar applications in order to avoid the unwantedstimulation of nerves and muscles that would result from the use of lowfrequency current. Lower frequencies may be used for bipolarapplications if the risk analysis shows the possibility of neuromuscularstimulation has been mitigated to an acceptable level. Normally,frequencies above 5 MHz are not used in order to minimize the problemsassociated with high frequency leakage currents. Higher frequencies may,however, be used in the case of bipolar applications. It is generallyrecognized that 10 mA is the lower threshold of thermal effects ontissue.

As discussed above, the electrosurgical device may be used inconjunction with a generator. The generator may be an electrosurgicalgenerator characterized by a fixed internal impedance and fixedoperating frequency that deliver maximum power to an external load(e.g., tissue), such as having an electrical impedance in the range ofabout 50 ohms to 150 ohms. In this type of bipolar electrosurgicalgenerator, the applied voltage may increase monotonically as the loadimpedance increases toward the maximum “open circuit” voltage as theload impedance increases to levels of tens of thousands of ohms or more.In addition, the electrosurgical device may be used with a bipolarelectrosurgical generator having a fixed operating frequency and anoutput voltage that may be substantially constant over a range of loadimpedances of tens of ohms to tens of thousands of ohms including “opencircuit” conditions. The electrosurgical device may be advantageouslyused with a bipolar electrosurgical generator of either a variablevoltage design or substantially constant voltage design in which theapplied voltage may be interrupted when the delivered current decreasesbelow a predetermined level. Such bipolar generators may be referred toas automatic generators in that they may sense the completion of thecoagulation process and terminate the application of voltage, oftenaccompanied by an audible indication in the form of a cessation of a“voltage application” tone or the annunciation of a unique “coagulationcomplete” tone. Further, the electrosurgical device may be used with anelectrosurgical generator whose operating frequency may vary with theload impedance as a means to modulate the applied voltage with changesin load impedance.

Various aspects of electrosurgical devices use therapeutic and/orsub-therapeutic electrical energy to treat tissue. Some aspects may beutilized in robotic applications. Some aspects may be adapted for use ina hand operated manner. In one non-limiting example, an electrosurgicaldevice may include a proximal handle, a distal working end or endeffector, and an introducer or elongated shaft disposed in-between.

Additional details regarding electrosurgical end effectors, jaw closingmechanisms, and electrosurgical energy-delivery surfaces are describedin the following U.S. patents and published patent applications: U.S.Pat. Nos. 7,087,054; 7,083,619; 7,070,597; 7,041,102; 7,011,657;6,929,644; 6,926,716; 6,913,579; 6,905,497; 6,802,843; 6,770,072;6,656,177; and 6,533,784; and U.S. Pat. App. Pub. Nos. 2010/0036370 and2009/0076506, all of which are incorporated herein by reference in theirentirety and made part of this specification.

FIG. 1A shows one example of a surgical instrument system 100, accordingto aspects of the present disclosure. The surgical instrument system 100comprises an electrosurgical instrument 110. The electrosurgicalinstrument 110 may comprise a proximal handle 112, a distal working endor end effector 200 and an introducer or elongated shaft 114 disposedin-between. Alternatively, the end effector may be attached directly tothe handle as in scissor style devices such as the electrosurgicalinstrument described in U.S. Pat. No. 7,582,087.

The electrosurgical system 100 can be configured to supply energy, suchas electrical energy, ultrasonic energy, heat energy, or any combinationthereof, to the tissue of a patient either independently orsimultaneously, for example. In one example, the electrosurgical system100 may include a generator 120 in electrical communication with theelectrosurgical instrument 110. The generator 120 may be connected tothe electrosurgical instrument 110 via a suitable transmission mediumsuch as a cable 122. In one example, the generator 120 may be coupled toa controller, such as a control unit 125, for example. In variousaspects, the control unit 125 may be formed integrally with thegenerator 120 or may be provided as a separate circuit module or deviceelectrically coupled to the generator 120 (shown in phantom toillustrate this option). The control unit 125 may include automated ormanually operated controls to control the amount of current delivered bythe generator 120 to the electrosurgical instrument 110. Although aspresently disclosed, the generator 120 is shown separate from theelectrosurgical instrument 110, in some aspects, the generator 120(and/or the control unit 125) may be formed integrally with theelectrosurgical instrument 110 to form a unitary electrosurgical system100, where a battery located within the electrosurgical instrument 110may be the energy source and a circuit coupled to the battery producesthe suitable electrical energy, ultrasonic energy, or heat energy.

In one aspect, the generator 120 may comprise an input device located ona front panel of the generator 120 console. The input device maycomprise any suitable device that generates signals suitable forprogramming the operation of the generator 120, such as a keyboard, orinput port, for example. In one example, one or more electrodes in thefirst jaw 210 a and one or more electrodes in the second jaw 210 b maybe coupled to the generator 120. The cable 122 may comprise multipleelectrical conductors for the application of electrical energy to afirst electrode (which may be designated as a + electrode) and to asecond electrode (which may be designated as a − electrode) of theelectrosurgical instrument 110. It may be recognized that + and −designations are made solely for convenience and do not indicate anelectrical polarity. An end of each of the conductors may be placed inelectrical communication with a terminal of the generator 120. Thegenerator 120 may have multiple terminals, each configured to contactone or more of the conductors. The control unit 125 may be used toactivate the generator 120, which may serve as an electrical source. Invarious aspects, the generator 120 may comprise an RF source, anultrasonic source, a direct current source, and/or any other suitabletype of electrical energy source, for example, which may be activatedindependently or simultaneously.

In various aspects, the electrosurgical system 100 may comprise at leastone supply conductor 131 and at least one return conductor 133, whereincurrent can be supplied to the electrosurgical instrument 110 via the atleast one supply conductor 131 and wherein the current can flow back tothe generator 120 via the at least one return conductor 133. In variousaspects, the at least one supply conductor 131 and the at least onereturn conductor 133 may comprise insulated wires and/or any othersuitable type of conductor. As described below, the at least one supplyconductor 131 and the at least one return conductor 133 may be containedwithin and/or may comprise the cable 122 extending between, or at leastpartially between, the generator 120 and the end effector 200 of theelectrosurgical instrument 110. The generator 120 can be configured toapply a sufficient voltage differential between the supply conductor 131and the return conductor 133 such that sufficient current can besupplied to the end effector 200 to perform the intended electrosurgicaloperation.

The shaft 114 may have a cylindrical or rectangular cross-section, forexample, and can comprise a thin-wall tubular sleeve that extends fromthe proximal handle 112. The shaft 114 may include a bore extendingtherethrough for carrying actuator mechanisms, for example, an axiallymoveable member for actuating the jaws 210 a, 210 b and for carryingelectrical leads for delivery of electrical energy to electrosurgicalcomponents of the end effector 200. The proximal handle 112 may includea jaw closure trigger 121 configured to adjust the position of the jaws210 a, 210 b with respect to each other. In one non-limiting example,the jaw closure trigger 121 may be coupled to an axially moveable memberdisposed within the shaft 114 by a shuttle operably engaged to anextension of the jaw closure trigger 121.

The end effector 200 may be adapted for capturing and transecting tissueand for contemporaneously welding the captured tissue with controlledapplication of energy (e.g., RF energy). The first jaw 210 a and thesecond jaw 210 b may be closed thereby capturing or engaging tissue. Thefirst jaw 210 a and second jaw 210 b also may apply compression to thetissue. In some aspects, the shaft 114, along with the first jaw 210 aand second jaw 210 b, can be rotated, for example, a full 360°. Forexample, a rotation knob 148 may be rotatable about the longitudinalaxis of the shaft 114 and may be coupled to the shaft 114 such thatrotation of the knob 148 causes corresponding rotation of the shaft 114.The first jaw 210 a and the second jaw 210 b can remain openable and/orcloseable while rotated.

Also illustrated in FIG. 1 are a knife advancement control 140 and anenergy activation control 145 located on the proximal handle 112. Insome non-limiting examples, the knife advancement control 140 and theenergy activation control 145 may be depressible buttons positioned topermit a user to control knife advancement or energy activation by theuse of one or more fingers.

FIG. 1B illustrates a second example of a surgical system 10 comprisinga generator 1002 and various surgical instruments 1004, 1006, 1202usable therewith, according to some aspects. The generator 1002 may beconfigurable for use with a variety of surgical devices. According tovarious forms, the generator 1002 may be configurable for use withdifferent surgical devices of different types including, for example,the ultrasonic device 1004, electrosurgical or RF surgical devices, suchas, the RF device 1006, and multifunction devices 1202 that integrateelectrosurgical RF and ultrasonic energies delivered simultaneously fromthe generator 1002. Although in the form of FIG. 1B, the generator 1002is shown separate from the surgical devices 1004, 1006, 1202 in oneform, the generator 1002 may be formed integrally with either of thesurgical devices 1004, 1006, 1202 to form a unitary surgical system. Thegenerator 1002 comprises an input device 1045 located on a front panelof the generator 1002 console. The input device 1045 may comprise anysuitable device that generates signals suitable for programming theoperation of the generator 1002. The generator 1002 may also comprise anoutput device 1047 (FIG. 1) located, for example, on a front panel ofthe generator 1002 console. The output device 1047 includes one or moredevices for providing a sensory feedback to a user. Such devices maycomprise, for example, visual feedback devices (e.g., an LCD displayscreen, LED indicators), audio feedback devices (e.g., a speaker, abuzzer) or tactile feedback devices (e.g., haptic actuators).

FIG. 1C illustrates one aspect of a surgical device 900 configured tograsp and cut tissue. The surgical device 900 can include a proximalhandle portion 910, a shaft portion 912, and an end effector 914configured to grasp tissue. The proximal handle portion 910 can be anytype of pistol-grip or other type of handle known in the art that isconfigured to carry various actuators 924, such as actuator levers,triggers or sliders, configured to actuate the end effector 914. Asillustrated, the proximal handle portion 910 can include a closure grip920 and a stationary grip 922. Movement of the closure grip 920 towardand away from the stationary grip 922, such as by manual movement by ahand of a user, can adjust a position of the end effector 914. The shaftportion 912 can extend distally from the proximal handle portion 910 andcan have a bore (not shown) extending therethrough. The bore can carrymechanisms for actuating the end effector 914, such as a jaw closuretube and/or a drive shaft. As discussed further below, one or moresensors (not shown) can be coupled to the surgical device 900 and can beconfigured to sense data that can be used in controlling an output ofthe device's motor 932. The device's motor 932 can be coupled to acontroller 934, which in turn may be coupled to the power source 936.

The end effector 914 can have a variety of sizes, shapes, andconfigurations. As shown in FIG. 1C, the end effector 914 can include afirst, upper jaw 16 a and a second, lower jaw 916 b each disposed at adistal end 912 d of the shaft portion 912. One or both of the upper andlower jaws 916 a, 916 b can be configured to close or approximate abouta longitudinal axis L1 of the end effector 914. Both of the jaws 916 a,916 b can be moveable relative to the shaft portion 912 such that theend effector 914 can be moved between open and closed positions, or onlyone the upper and lower jaws 916 a, 916 b can be configured to moverelative to the shaft portion 912 and to the other of the jaws 916 a,916 b so as to move the end effector 914 between open and closedpositions. When the end effector 914 is in the open position, the jaws916 a, 916 b can be positioned at a distance apart from one another withspace therebetween. As discussed further below, tissue can be positionedwithin the space between the jaws 916 a, 916 b. When the end effector914 is in the closed position, a longitudinal axis of the upper jaw 916a can be substantially parallel to a longitudinal axis of the lower jaw916 b, and the jaws 916 a, 916 b can be moved toward one another suchthat the distance therebetween is less than when the end effector 914 isin the open position. In some aspects, facing engagement surfaces 919 a,919 b of the jaws 916 a, 916 b can be in direct contact with one anotherwhen the end effector 914 is in the closed position such that thedistance between is substantially zero. As illustrated, the upper jaw 16a is configured to pivot relative to the shaft portion 912 and relativeto the lower jaw 916 b while the lower jaw 916 b remains stationary. Asillustrated, the jaws 916 a, 916 b have a substantially elongate andstraight shape, but a person skilled in the art will appreciate that oneor both of the jaws 916 a, 916 b can be curved along the longitudinalaxis L1 of the end effector 914. The longitudinal axis L1 of the endeffector 914 can be parallel to and coaxial with a longitudinal axis ofthe shaft portion 912 at least when the end effector 914 is in theclosed configuration, and if the end effector 914 is configured toarticulate relative to the shaft portion 912, when the end effector 914is not articulated relative to the shaft portion 912.

FIG. 1D illustrates another aspect of a surgical device 1400 configuredto cut and seal tissue clamped between first and second jaws 1402 a,1402 b of the device's end effector 1404. The device 1400 can beconfigured to separately cut and seal tissue and configured tosimultaneously cut and seal tissue, with a user of the device 1400 beingable to decide whether cutting and sealing occurs separately orsimultaneously. The device 1400 can generally be configured similar tothe device 900 of FIG. 1C. The device 1400 can include a motor 1406, aclosure trigger 1408, a firing actuator 1410, a controller 1412, acutting element (not shown), a power connector (not shown) configured toattach to an external power source (not shown), an energy actuator 1414,an elongate shaft 1416 extending from a handle portion 1418 of thedevice 1400, a sensor 1420 a, 1420 b, the end effector 1404 at a distalend of the shaft 1416, a stationary handle 1424, and a gear box 1426that can be operatively connected to the motor 1406 and configured totransfer output from the motor 1406 to the cutting element. Asillustrated, the controller 1412 includes a printed circuit board (PCB),the sensor 1420 a includes a Hall effect sensor, and the other sensor1420 b includes a Hall effect sensor. One of the jaws 1420 a includes aninsulator 1428 configured to facilitate safe energy application totissue clamped by the end effector 1404. Each of the jaws 1402 a, 1402 bcan include a proximal slot 1430 a, 1430 b configured to facilitateopening and closing of the end effector 1404, as will be appreciated bya person skilled in the art. The device 1400 can be configured to lockthe closure trigger 1408 in the closed position, such as by the closuretrigger 1408 including a latch 1432 configured to engage a correspondinglatch 1434 on the stationary handle 1424 when the closure trigger 1408is drawn close enough thereto so as to lock the closure trigger 1408 inposition relative to the stationary handle 1424. The closure triggerlatch 1432 can be configured to be manually released by a user so as tounlock and release the closure trigger 1408. A bias spring 1436 includedin the handle portion 1418 can be coupled to the closure trigger 1408and cause the closure trigger 1408 to open, e.g., move away from thestationary handle 1424, when the closure trigger 1408 is unlocked.

FIG. 2 shows a perspective view of the end effector 200 with the jaws210 a, 210 b open, according to one aspect of the present disclosure.The end effector 200 may be attached to any of the various surgicalinstruments provided herein, including those configured to supply RFenergy, ultrasonic energy, or various combinations of energy to the endeffector 200. The end effector 200 may comprise the first or upper jaw210 a and the second or lower jaw 210 b, which may be straight orcurved. The upper jaw 210 a may comprise a first distal end 212 a and afirst proximal end 214 a. The lower jaw 210 b may comprise a seconddistal end 212 b and a second proximal end 214 b. The first distal end212 a and the second distal end 212 b may be collectively referred to asthe distal end of the end effector when the jaws 210 a, 210 b are in aclosed configuration. The first proximal end 214 a and the secondproximal end 214 b may be collectively referred to as the proximal endof the end effector 200. The jaws 210 a, 210 b are pivotally coupled atthe first and second proximal ends 214 a, 214 b. As shown in FIG. 2, Thelower jaw 210 b is fixed and the upper jaw 210 a is pivotally movablerelative to the lower jaw 210 b from an open position to a closedposition and vice versa. In the closed position, the first and seconddistal ends 212 a, 212 b are in proximity. In the open position, thefirst and second distal ends 214 a, 214 b are spaced apart. In otheraspects, the upper jaw 210 a may be fixed and the lower jaw 210 b may bemovable. In other aspects, both the upper and lower jaws 210 a, 210 bmay be movable. The end effector 200 may comprise a pivot assembly 270located at or in proximity to the proximal end of the end effector,which sets an initial gap between the jaws 210 a, 210 b at the proximalend of the end effector 200 in a closed position.

In some aspects, the first jaw 210 a and the second jaw 210 b may eachcomprise an elongated slot or channel 250 a and 250 b, respectively,disposed along their respective middle portions. The channels 250 a and250 b may be sized and configured to accommodate the movement of anaxially moveable member (not shown), which may comprise a tissue-cuttingelement, for example, comprising a sharp distal edge. The upper jaw 210a may comprise a first energy delivery surface 230 a. The lower jaw 210b may comprise a second energy delivery surface 230 b. The first andsecond energy delivery surfaces 230 a, 230 b face each other when thejaws 210 a, 210 b are in a closed configuration. The first energydelivery surface 230 a may extend in a “U” shape around the channel 250a, connecting at the first distal end 212 a. The second energy deliverysurface 230 b may extend in a “U” shape around the channel 250 b,connecting at the second distal end 212 b. The first and second energydelivery surfaces 230 a, 230 b may comprise electrically conductivematerial such as copper, gold plated copper, silver, platinum, stainlesssteel, aluminum, or any suitable electrically conductive biocompatiblematerial, for example. The second energy delivery surface 230 b may beconnected to the supply conductor 131 shown in FIG. 1A, for example,thus forming the first electrode 220 in the electrosurgical instrument110. The first energy delivery surface 230 a may be connected and thereturn conductor 133 shown in FIG. 1A, thus forming the second electrode222 the electrosurgical instrument 110. For example, the first energydelivery surface 230 a may be grounded. Opposite connection is alsopossible. The first and second electrodes 220, 222 can be configured topass energy through tissue positioned between the electrodes 220, 222.The energy may comprise, for example, radiofrequency (RF) energy,sub-therapeutic RF energy, therapeutic RF energy, ultrasonic energy,and/or other suitable forms of energy.

As shown in FIG. 2, the second energy delivery surface 230 b is formedby a conductive layer disposed, or at least partially disposed, along atleast a portion of the body of the lower jaw 210 b. The electricallyconductive layer comprising the second energy delivery surface 230 b mayextend to the second distal end 212 b, and thus operation of the endeffector 200 is possible without actually grasping the tissue. The lowerjaw 210 b may further comprise an electrically insulative layer 260arranged between the conductive layer and the body of the lower jaw 210b. The electrically insulative layer 260 may comprise electricallyinsulative material such as ceramic or nylon. Furthermore, the firstenergy delivery surface 230 a is formed of an electrically conductivelayer disposed, or at least partially disposed, along at least a portionof the body of the upper jaw 210 a. The upper jaw 210 a also maycomprise an electrically insulative layer arranged between theconductive layer and the body of the upper jaw 210 a.

The upper and lower jaws 210 a and 210 b may each comprise one or moreelectrically insulative tissue engaging members arranged on the first orsecond energy delivery surface 230 a, 230 b, respectively. Each of theelectrically insulative tissue engaging members may protrude from theenergy delivery surface and define a height above the energy deliverysurface, and thus is sometimes referred to as a “tooth.” Theelectrically insulative tissue engaging members may compriseelectrically insulative material such as ceramic or nylon. As shown inFIG. 2, the electrically insulative tissue engaging members 240 arearranged longitudinally, e.g., along the length of the lower jaw 210 b,from the send proximal end 214 b to the second distal end 212 b and onthe second energy delivery surface 230 b. As shown in FIG. 2, theelectrically insulative tissue engaging members 240 are in pairs, andeach pair is arranged next to the channel 250 b and is separated by thechannel 250 b. These paired electrically insulative tissue engagingmembers 240 as arranged here are sometimes referred to as “teeth.”

In other aspects, other configurations of the electrically insulativetissue engaging members 240 are possible. For example, the electricallyinsulative tissue engaging members 240 may be located at a distance awayfrom the channel. For example, the electrically insulative tissueengaging members 240 may be arranged in a grid on the energy deliverysurface. In other aspects, the electrically insulative tissue engagingmembers 240 may not have the half cylindrical cross sections as shown inFIG. 2, and may have cylindrical cross sections or rectangular crosssections. In other aspects, electrically insulative tissue engagingmembers 240 may be arranged on the first energy delivery surface 230 a,or may be arranged on both of the first and second energy deliverysurfaces 230 a, 230 b.

FIG. 3 is a block diagram of a surgical system 300 comprising amotor-driven surgical grasping instrument 900, 1400 (FIGS. 10, 1D)according to some aspects of the present disclosure, the surgicalinstrument coupled to a generator 335 (340), according to some aspects.The motor-driven surgical cutting and fastening instrument 2 describedin the present disclosure may be coupled to a generator 335 (340)configured to supply power to the surgical instrument through externalor internal means. FIG. 3 describes examples of the portions for howelectrosurgical energy may be delivered to the end effector. In certaininstances, the motor-driven surgical instrument 110 may include amicrocontroller 315 coupled to an external wired generator 335 orinternal generator 340. Either the external generator 335 or theinternal generator 340 may be coupled to A/C mains or may be batteryoperated or combinations thereof. The electrical and electronic circuitelements associated with the motor-driven surgical instrument 110 and/orthe generator elements 335, 340 may be supported by a control circuitboard assembly, for example. The microcontroller 315 may generallycomprise a memory 310 and a microprocessor 305 (“processor”)operationally coupled to the memory 310. The microcontroller 315 may beconfigured to regulate the electrosurgical energy applied at the endeffector according to the concepts disclosed herein and described morebelow. The processor 305 may control a motor driver 320 circuitgenerally utilized to control the position and velocity of the motor325. The motor 325 may be configured to control transmission of energyto the electrodes at the end effector of the surgical instrument. Incertain instances, the processor 305 can signal the motor driver 320 tostop and/or disable the motor 325, as described in greater detail below.In certain instances, the processor 305 may control a separate motoroverride circuit which may comprise a motor override switch that canstop and/or disable the motor 325 during operation of the surgicalinstrument in response to an override signal from the processor 305. Theprocessor may be communicatively coupled to a display/indicator 330. Itshould be understood that the term processor as used herein includes anysuitable microprocessor, microcontroller, or other basic computingdevice that incorporates the functions of a computer's centralprocessing unit (CPU) on an integrated circuit or at most a fewintegrated circuits. The processor is a multipurpose, programmabledevice that accepts digital data as input, processes it according toinstructions stored in its memory, and provides results as output. It isan example of sequential digital logic, as it has internal memory.Processors operate on numbers and symbols represented in the binarynumeral system.

In some cases, the processor 305 may be any single core or multicoreprocessor such as those known under the trade name ARM Cortex by TexasInstruments. In some cases, any of the surgical instruments of thepresent disclosures may comprise a safety processor such as, forexample, a safety microcontroller platform comprising twomicrocontroller-based families such as TMS570 and RM4x known under thetrade name Hercules ARM Cortex R4, also by Texas Instruments.Nevertheless, other suitable substitutes for microcontrollers and safetyprocessor may be employed, without limitation. In one instance, thesafety processor may be configured specifically for IEC 61508 and ISO26262 safety critical applications, among others, to provide advancedintegrated safety features while delivering scalable performance,connectivity, and memory options.

In certain instances, the microcontroller 315 may be an LM 4F230H5QR,available from Texas Instruments, for example. In at least one example,the Texas Instruments LM4F230H5QR is an ARM Cortex-M4F Processor Corecomprising on-chip memory 310 of 256 KB single-cycle flash memory, orother non-volatile memory, up to 40 MHz, a prefetch buffer to improveperformance above 40 MHz, a 32 KB single-cycle serial random accessmemory (SRAM), internal read-only memory (ROM) loaded withStellarisWare® software, 2 KB electrically erasable programmableread-only memory (EEPROM), one or more pulse width modulation (PWM)modules, one or more quadrature encoder inputs (QEI) analog, one or more12-bit Analog-to-Digital Converters (ADC) with 12 analog input channels,among other features that are readily available for the productdatasheet. Other microcontrollers may be readily substituted for use inthe motor-driven surgical instrument 110. Accordingly, the presentdisclosure should not be limited in this context.

Referring again to FIG. 3, the surgical system 300 may include a wiredgenerator 335, for example. In certain instances, the wired generator335 may be configured to supply power through external means, such asthrough electrical wire coupled to an external generator. In some cases,the surgical system 300 also may include or alternatively include aninternal generator 340. The internal generator 340 may be configured tosupply power through internal means, such as through battery power orother stored capacitive source. Further descriptions of the internalgenerator 340 and the wired generator 335 are described below.

In certain instances, the motor-driven surgical instrument 110 maycomprise one or more embedded applications implemented as firmware,software, hardware, or any combination thereof. In certain instances,the motor-driven surgical instrument 110 may comprise various executablemodules such as software, programs, data, drivers, and/or applicationprogram interfaces (APIs), for example.

Referring to FIG. 4A, graph 400 and provides a visual depiction of thelevel of impedance over time present in tissue undergoing a sealingprocedure during surgery. This example graph 400 provides a conceptualframework for the types of power adjustments employed according to thepresent disclosures. Here, time zero represents the first point at whicha surgical instrument, such as instrument 110, applies electrosurgicalenergy to tissue at a surgical site. The Y axis represents the level oftissue impedance (Z) present when a substantially constant level ofpower is applied to the tissue via an end effector of the instrument110. At time zero, the tissue exhibits an initial level of impedance(Z_(init)) 410. The initial level of impedance 410 may be based onnative physiological properties about the tissue, such as density,amount of moisture, and what type of tissue it is. Over a short periodof time, it is known that the level of impedance actually dips slightlyas power is continuously applied to the tissue. This is a commonphenomenon that occurs in all kinds of tissue. A minimum level ofimpedance (Z_(min)) 420 is eventually reached. From here, the overalllevel of impedance monotonically increases, and at first increases witha slow rise. Eventually, a transition point is reached such that levelof impedance starts to dramatically rise above the initial level ofimpedance 410. This point is generally known as a transition impedancelevel (Z_(trans)) 430. After the transition impedance 430 is reached,the level of impedance rises dramatically over time, and beyond thispoint the tissue impedance is generally too high for electrosurgicalenergy to have a substantial impact on the tissue. Therefore,termination 440 of the electrosurgical energy generally occurs soonafter the transition impedance 430 point is reached. Thus, the period oftime between the initial impedance 410 and when the transition impedance430 is reached is generally the only effective time when electrosurgicalenergy may be applied to the tissue with any positive effect. Thisregion is sometimes known as the bathtub region 450, due to the generalshape of the curve over this time period. It is therefore desirableextend or prolong the bathtub region 450 in order to increase the amountof time where electrosurgical energy may be applied.

Referring to FIG. 4B, graph 450 shows an example of a typical load curvefor a generator configured to provide power to an electrosurgical systemof the present disclosure. The left vertical axis represents power (W)and voltage (V), the right vertical axis represents current (A), and thehorizontal axis represents load impedance (Ohms). The voltage curve 452,current curve 454, and power curve 456 are shown as functions of loadimpedance. As shown, the amount of power and voltage applied to tissuetypically reaches an impassable threshold, even over ever increasingload impedances. Looked at another way, the amount of energy applied tothe tissue at a surgical site has a noticeable effect only up to certainlevels of load impedances, and after a certain impedance threshold, suchas 175 ohms, applying more or sustained power typically has little to nobenefit. Graph 450 therefore provides further detail on why exceedingthe transition impedance threshold, as shown in graph 400, generallyrepresents the cutoff point to which power should continue to beapplied.

Referring to FIG. 5, graph 500 provides another example of the level oftissue impedance over time, this time using more empirical data. Asshown, the level of tissue impedance stays relatively low until thetransition impedance level is reached, which occurs a little after fourseconds in this example. In some cases, the transition impedance levelis defined by the point at which the level of impedance rises abovetwice the value of the minimum impedance level, while in other cases itmay be defined as the point at which the initial impedance level isreached again. Regardless of which definition is used, the transitionimpedance level generally occurs at around the same time, assuming aconstant level of power is applied to the tissue. Furthermore, it isknown that the transition impedance level is reliably a function of theinitial impedance level of the tissue. In other words, depending on whatthe initial level of impedance is, the transition impedance level can bepredicted reliably in the tissue.

Referring to FIG. 6A, graph 600 illustrates an example power profile ofan amount of electrosurgical energy applied by a surgical instrument 110to tissue at a surgical site over time, in order to extend or prolongthe bathtub region, according to some aspects. The continuous, piecewisecurve 610 shows that the level of power changes in multiple stages.Initially, the electrosurgical energy applied rises to a predeterminedlevel of power, such as 20 W in this case. This represents the initialdesired level of power used for the surgical procedure in question.While the tissue impedance is generally in the bathtub region, thisinitial level of power is acceptable. However, as the tissue impedancebegins to change and rises toward the transition impedance level,according to some aspects, the level of power is tapered down at asteady rate, rather than the level of power be constantly maintainedlike in conventional methods. In this example, it is supposed that thetransition impedance level is 200 ohms, and may have been determinedbased on a measurement of the initial impedance level. Thus, as thetissue impedance rises but before it reaches the transition impedancelevel, such as when the tissue impedance reaches 75% of the transitionimpedance level (i.e., 150 ohms), the power system of the surgicalinstrument 110 may cause the level of power to decrease at a steadyrate, as shown in the downward sloped region 620. For example, the powerlevel may be dropped by 50% over the course of time where the tissueimpedance level continues to climb until it reaches the transitionimpedance level. Finally, once the transition impedance level isreached, the power to the surgical instrument 110 may be cutdramatically, as further application of power beyond the transitionimpedance level may be ineffective or may even cause unwanted damage tothe tissue. In some aspects, the tapering of the power may be achievedin a number of ways that are all within the purview of this disclosure.For example, the microprocessor 315 (see FIG. 3) may regulate the powercoming from generators 335 or 340 via pulse width modulation or byapplying an increase in resistance via the driver 320. In general, thepresent disclosures may employ any methods for lowering the power knownto those with skill in the art, and aspects are not so limited.

Referring to FIG. 6B, graph 650 shows an example adjusted impedanceprofile over time as a result of the adjusted power applied to thesurgical instrument 110, such as the example power profile 610,according to some aspects. As shown, the rise in impedance out of thebathtub region may be made more gradual due to the tapering of the powermade according to aspects of the present disclosure. In addition, theoverall length of the bathtub region may be extended or prolonged. Thegradual rise of the tissue impedance may also allow for better care andtreatment of the tissue under surgery. Conventionally, continuous powerapplied to the tissue after the transition impedance level is reachedmay cause unwanted damage to the tissue, such as burning tissue,sizzling, and popping. Due to the adjustments disclosed herein, thisunwanted damage may be reduced or even eliminated.

Referring to FIG. 7, graph 700 shows an example power profile of thetapered load curve concept introduced in FIG. 6A, with additional powercharacteristics superimposed. Here, the curve 710 as shown by the thickline represents a measure of voltage as a function of load impedance inthe tissue. The curve 720 as shown by the medium line represents ameasure of calculated power applied to the tissue as a function of loadimpedance. The calculated power may be the measure of power that isdetermined by the power system of the surgical instrument 110, while thecurve 730 as shown by the dashed line represents the actual or effectivepower applied to the tissue. As shown, both of these curves exhibit apower taper that is reduced in a stepwise manner. This may be caused bythe power being duty cycled at different rates over time, i.e., viapulse width modulation. The curve 740 as shown by the thin linerepresents a measure of current. The scale for the current is shown onthe right-hand side, while the scale for power and voltage is shown onthe left.

As shown, the power is tapered off in this example when the loadimpedance is measured to be approximately 60 to 70 ohms, and the poweris nearly completely cut off when the load impedance is measured to beabout 100 ohms. The voltage drops dramatically during the tapered regionof the power profile, but begins to slowly rise again due to the low butconstant application of power applied while the load impedance continuesto increase. Practically, the power may be cut off long before the loadimpedance reaches these higher levels.

Referring to FIG. 8, in some aspects, the surgical instrument 110 may beconfigured to apply different power algorithms to manage the rise oftissue impedance, based on varying levels of initial tissue impedance atthe surgical site. The flowchart 800 provides an example of how multipleload curves may be programmed into the surgical instrument 110 to applydifferent power adjustments based on impedance measurements during thesealing procedures. For example, an algorithm to adjust the power maybegin at block 810 that includes applying power to the end effector andultimately to the tissue in question at the surgical site. At block 820,while the end effector is applying the electrosurgical energy to thetissue, the impedance may be measured, and the minimum impedance may bedetermined based on the point at which the impedance eventually beginsto rise. The end effector may include one or more sensors configured tomonitor the impedance, voltage, or current, and may apply a number ofmathematical formulas to determine what the measured impedance is.Various examples for how the tissue impedance may be measured aredescribed in U.S. patent application Ser. Nos. 14/230,349 and14/660,620, which are incorporated herein by reference.

In this example, three different power profiles may be available to beapplied to the tissue, based on the measured level of minimum impedance:low, medium, and high. In this example, at block 830, the low minimumimpedance threshold is defined as when the minimum impedance is lessthan 30 ohms. At block 840, the medium minimum impedance threshold isdefined as when the minimum impedance is between 30 and 70 ohms. Atblock 850, the high minimum impedance threshold is defined as when theminimum impedance is greater than 70 ohms. Based on the measured minimumimpedance falling into one of these three categories, the load curve maybe adjusted according to three characteristics. For example, iffollowing the low minimum impedance profile, the power level in thebathtub region may be set to a maximum available power level (e.g., 30W), the transition impedance threshold may be defined as 30 ohms greaterthan the measured minimum impedance, and the impedance at which allpower is terminated may be set to 250 ohms. Based on these threecharacteristics, the power load curve may be generated. Examples ofthese different load curves are visually depicted in FIGS. 9 and 10,below. As another example, if following the medium minimum impedanceprofile, the power level in the bathtub may be set to a moderateavailable power level (e.g., 20 W), the transition impedance thresholdmay be defined as 50 ohms greater than the measured minimum impedance,and the impedance at which all power is terminated may be set to 300ohms. As a third example, if following the high minimum impedanceprofile, the power level in the bathtub region may be set to a lowavailable power level (e.g., 10 W), the transition impedance thresholdmay be defined as 100 ohms greater than the measured minimum impedance,and the impedance at which all power is terminated may be set to 400ohms.

In some aspects, rather than the minimum impedance being measured, andinitial impedance may be measured and the load curves may be variedbased on measured initial impedance levels. It may be apparent to thosewith skill in the art how the examples provided herein may be modifiedto account for an initial impedance level being measured, rather thanthe minimum impedance level being measured. For example, the calculationof the transition impedance may be offset by a different factor toaccount for the difference in value between the minimum impedance andthe initial impedance. In addition, the thresholds under which thedifferent load curves may be followed (e.g., blocks 830, 840, and 850)may be based on modified criteria according to the different ranges ofinitial impedance.

The power system in the medical instrument 110 may apply power to thetissue according to the load curve, depending on which load curve ischosen. In all cases, the power system may be configured to taper thepower and the bathtub region as the impedance begins to slowly risetoward the transition impedance level, consistent with the conceptsdescribed in FIGS. 6A and 7.

Once the medical instrument 110 has finished applying power according toone of the load curves, a termination procedure may be executed at block860. In some aspects, the termination power sequence may be based onwhat termination impedance value was set in the previous blocks offlowchart 800. For example, a series of termination pulses may betransmitted to the end effector of the medical instrument 110.

Referring to FIG. 9, a visual depiction of an example load curve underthe low minimum impedance threshold is shown (see FIG. 8), according tosome aspects. In this example, it may have been determined that theminimum impedance is 20 ohms, and therefore that the transitionimpedance level is 50 ohms (i.e., 30 ohms greater than the minimumimpedance). The power level in the bathtub region may be set to amaximum level, such as 30 W. After the transition impedance level isreached, the power level may be dropped to a minimum, and may beultimately terminated once the impedance reaches 250 ohms (not shown).In some aspects, the power level is dramatically cut once the transitionimpedance level is reached, while in other cases the power level may betapered to decrease more gradually prior to the transition impedancebeing reached.

Referring to FIG. 10, a visual depiction of an example load curve underthe moderate impedance threshold is shown (see FIG. 8), according tosome aspects. In this example, it may have been determined that theminimum impedance is 50 ohms, and therefore that the transitionimpedance level is 100 ohms (i.e., 50 ohms greater than the minimumimpedance). The power level in the bathtub region may be set to amoderate level, such as 20 W. After the transition impedance level isreached, the power level may be dropped to a minimum, and may beultimately terminated once the impedance reaches 300 ohms (not shown).In some aspects, the power level is dramatically cut once the transitionimpedance level is reached, while in other cases the power level may betapered to decrease more gradually prior to the transition impedancebeing reached.

In general, the example power algorithms and concepts from which theseexamples are based on may be adapted to many different types ofelectrode configurations, and aspects are not so limited. Variousexamples include electrodes of various length and width, includingwider, narrower, longer or shorter electrodes than the examples shownherein; electrodes using I-Beam technology; motorized electrosurgicalsystems (similar to those described herein); scissor-type electrodes;and hand-held forceps-like instruments, whether open, laparoscopic orrobotic. The power algorithms described herein may be set and adapted tothese different scenarios by adjusting the various parameters as shownand described herein.

FIG. 11 is a graphical illustration 1100 of impedance threshold andminimum pulse duration showing an example of additional adjustments thatcan be made to varying the power to account for other tissue properties,according to one aspect of the present disclosure. The vertical axisrepresents, from left to right, Voltage (rms), Current (rms), Power (W),and Impedance (Ohms)/Energy (J) and the horizontal axis represents Time.Accordingly, a voltage curve 1102, current curve 1104, power curve 1106,and impedance/energy curve 1108 are shown superimposed as a function oftime. Referring to FIG. 11, the illustration 1100 shows an example ofadditional adjustments that can be made to varying the power, in orderto account for other tissue properties. The illustration 1100 showsexample impedance thresholds and minimum pulse durations over time,along with corresponding levels of power, voltage and current. In someaspects, the initial power level applied to the tissue may be based onadditional factors, and the power adjustments may be varied to prolongthe bathtub region based on these initial varied power levels, accordingto some aspects. For example, fatty tissues tend to have higherimpedances during sealing. These impedances are often greater than 50ohms after the initial pulses of energy are delivered to the tissue.Without accounting for these tissue properties, if the tissue impedanceis greater than 50 ohms, the tissue will not receive full power from thegenerator. In response, increasing this threshold from 50 to 125 ohms(see circle 1 in illustration 1100) may enable the generator to deliverfull power into the base mesentery, thus reducing sealing cycle time. Inthis case, if human tissue is more resistive than 125 ohms, then longseal times could occur. The threshold may be therefore need to beincreased beyond 125 ohms in other circumstances.

Regarding minimum pulse duration, it has been observed that with short180 millisecond (ms) pulses, the impedance (black curve, e.g., curvewithin circle 1) tends to stall and not rise quickly (see the movementof this curve within the time span under circle 2). In order to allowthe tissue impedance to increase, the duration of the pulse on time canbe increased. Thus, in some aspects, the minimum pulse width may beincreased from 180 ms to 480 ms for composite load curve (CLC) tables.

FIG. 12 is a graphical illustration 1200 of voltage cutback caused by animpedance threshold greater than 325 Ohms, according to one aspect ofthe present invention. As shown, the voltage curve 1102 based on the CLCtable bounces between 60 and 100 Volts (see circle 3 in illustration1100) as tissue impedance approaches a 300 Ohm termination impedance.This bouncing causes the impedance rise rate to slow down as can be seenin the bouncing impedance/energy curve 1108. The voltage cutback iscaused by a 325 Ohm threshold programmed in the original algorithm. Ifthe 325 Ohm threshold is exceeded, the generator is configured to reducethe applied voltage from 100 volts to 60 volts. Accordingly, one aspectof the algorithm described herein does not include an impedancethreshold that is greater than 325 Ohms.

FIG. 13 is a graphical illustration 1300 of a power pulse region of thegraphical illustration 1100 shown in FIG. 11, according to one aspect ofthe present disclosure. In one aspect, the algorithm is configured suchthat the duration of the power pulse is 1 second for each step of thevoltage curve 1102. It was observed that during the later half of each 1second pulse the rise rate (slope) of the impedance curve 1108 woulddecrease (see circle 4 in illustration 1300). Accordingly, in one aspectof the algorithm, the duration of the power pulse is decreased to 0.5seconds for each step of the voltage curve 1102 to prevent the impedancetrajectory from stalling during the power pulse. In accordance with the0.5 seconds duration of the power pulse, the number of power pulses isreduced from 4 to 3 (see circle 5 in illustration 1300). The duration ofeach power pulse remains 1 second. This allows tissue which is doneearlier to proceed through the algorithm and thus finish sooner.

In general, aspects of the present disclosure may allow for varioustypes of adjustments to be made to the amount of electrosurgical energyapplied to the tissue at the surgical site, based on measured levels ofimpedance in the surgical tissue. For example, the power algorithms madediffer if the type of energy applied to the surgical tissue includes RFenergy versus ultrasonic energy. The various characteristics of the loadcurves may need to be adjusted, e.g., what the maximum power level canbe set to, what should the transition impedance be set to, when shouldthe energy be terminated, at what level impedance should the power beginto taper off, etc., due to how the tissue may respond based on thedifferent types of energy being applied to it. However, in general, thegeneral shapes of the power profiles should remain consistent, and itmay simply be a matter of determining what values should be set for thecritical characteristics of the load curves, based on a measured minimumimpedance or initial impedance, and in some aspects also based onvarious other characteristics of the types of energy applied to thetissue.

In some cases, various aspects may be implemented as an article ofmanufacture. The article of manufacture may include a computer readablestorage medium arranged to store logic, instructions and/or data forperforming various operations of one or more aspects. In variousaspects, for example, the article of manufacture may comprise a magneticdisk, optical disk, flash memory or firmware containing computer programinstructions suitable for execution by a general purpose processor orapplication specific processor. The aspects, however, are not limited inthis context.

The functions of the various functional elements, logical blocks,modules, and circuits elements described in connection with the aspectsdisclosed herein may be implemented in the general context of computerexecutable instructions, such as software, control modules, logic,and/or logic modules executed by the processing unit. Generally,software, control modules, logic, and/or logic modules comprise anysoftware element arranged to perform particular operations. Software,control modules, logic, and/or logic modules can comprise routines,programs, objects, components, data structures, and the like thatperform particular tasks or implement particular abstract data types. Animplementation of the software, control modules, logic, and/or logicmodules and techniques may be stored on and/or transmitted across someform of computer-readable media. In this regard, computer-readable mediacan be any available medium or media useable to store information andaccessible by a computing device. Some aspects also may be practiced indistributed computing environments where operations are performed by oneor more remote processing devices that are linked through acommunications network. In a distributed computing environment,software, control modules, logic, and/or logic modules may be located inboth local and remote computer storage media including memory storagedevices.

Additionally, it is to be appreciated that the aspects described hereinillustrate example implementations, and that the functional elements,logical blocks, modules, and circuits elements may be implemented invarious other ways which are consistent with the described aspects.Furthermore, the operations performed by such functional elements,logical blocks, modules, and circuits elements may be combined and/orseparated for a given implementation and may be performed by a greaternumber or fewer number of components or modules. As will be apparent tothose of skill in the art upon reading the present disclosure, each ofthe individual aspects described and illustrated herein has discretecomponents and features which may be readily separated from or combinedwith the features of any of the other several aspects without departingfrom the scope of the present disclosure. Any recited method can becarried out in the order of events recited or in any other order whichis logically possible.

Unless specifically stated otherwise, it may be appreciated that termssuch as “processing,” “computing,” “calculating,” “determining,” or thelike, refer to the action and/or processes of a computer or computingsystem, or similar electronic computing device, such as a generalpurpose processor, a DSP, ASIC, FPGA, or other programmable logicdevice, discrete gate or transistor logic, discrete hardware components,or any combination thereof designed to perform the functions describedherein that manipulates and/or transforms data represented as physicalquantities (e.g., electronic) within registers and/or memories intoother data similarly represented as physical quantities within thememories, registers, or other such information storage, transmission, ordisplay devices.

It is worthy to note that some aspects may be described using theexpression “coupled” and “connected” along with their derivatives. Theseterms are not intended as synonyms for each other. For example, someaspects may be described using the terms “connected” and/or “coupled” toindicate that two or more elements are in direct physical or electricalcontact with each other. The term “coupled,” however, also may mean thattwo or more elements are not in direct contact with each other, but yetstill co-operate or interact with each other. With respect to softwareelements, for example, the term “coupled” may refer to interfaces,message interfaces, and application program interface, exchangingmessages, and so forth.

The devices disclosed herein can be designed to be disposed of after asingle use, or they can be designed to be used multiple times. In eithercase, however, the device can be reconditioned for reuse after at leastone use. Reconditioning can include any combination of the steps ofdisassembly of the device, followed by cleaning or replacement ofparticular pieces, and subsequent reassembly. In particular, the devicecan be disassembled, and any number of the particular pieces or parts ofthe device can be selectively replaced or removed in any combination.Upon cleaning and/or replacement of particular parts, the device can bereassembled for subsequent use either at a reconditioning facility, orby a surgical team immediately prior to a surgical procedure. Thoseskilled in the art will appreciate that reconditioning of a device canutilize a variety of techniques for disassembly, cleaning/replacement,and reassembly. Use of such techniques, and the resulting reconditioneddevice, are all within the scope of the present application.

Although various aspects have been described herein, many modifications,variations, substitutions, changes, and equivalents to those aspects maybe implemented and will occur to those skilled in the art. Also, wherematerials are disclosed for certain components, other materials may beused. It is therefore to be understood that the foregoing descriptionand the appended claims are intended to cover all such modifications andvariations as falling within the scope of the disclosed aspects. Thefollowing claims are intended to cover all such modification andvariations.

The invention claimed is:
 1. A surgical system comprising: an endeffector comprising at least one energy delivery component configured totransmit electrosurgical energy to tissue at a surgical site; and acontrol circuit communicatively coupled to the at least one energydelivery component and programmed to: for a first application period,cause the at least one energy delivery component to transmit theelectrosurgical energy at a first power level, the first applicationperiod comprising a point in time where impedance of the tissue reachesa minimum impedance value; for a second application period after thefirst application period, cause the at least one energy deliverycomponent to transmit the electrosurgical energy, starting from apredetermined proportion of a transition impedance threshold level anddecreasing the electrosurgical energy at a steady rate from the firstpower level until a second power level is reached, wherein the secondpower level is lower than the first power level and the secondapplication period comprises a point in time where the impedance of thetissue rises above the minimum impedance value; and for a thirdapplication period after the second application period, directly afterreaching the second power level, cause the at least one energy deliverycomponent to reduce the second power level to a third power level whilemaintaining a constant level of the impedance of the tissue to transmitthe electrosurgical energy at the third power level upon the impedanceof the tissue reaching the transition impedance threshold level, thethird power level lower than the second power level and the thirdapplication period comprising a point in time where the impedance of thetissue rises above the transition impedance threshold level.
 2. Thesurgical system of claim 1, wherein the first application period and thesecond application period combined comprise a time period where theelectrosurgical energy is delivered at a higher rate and causes sealingof the tissue at the surgical site.
 3. The surgical system of claim 1,wherein the third application period further comprises a time periodwhere the impedance of the tissue rises to a level such that theelectrosurgical energy is delivered at a lower rate and no longer causessealing of the tissue at the surgical site.
 4. The surgical system ofclaim 1, further comprising at least one sensor configured to measure aninitial level of impedance in the tissue and the minimum impedance valuein the tissue.
 5. The surgical system of claim 4, wherein the controlcircuit is further programmed to determine a beginning of the thirdapplication period based on the measured initial level of impedance inthe tissue.
 6. The surgical system of claim 4, wherein the controlcircuit is further programmed to determine a beginning of the thirdapplication period based on the measured minimum impedance value in thetissue.
 7. The surgical system of claim 1, wherein the first applicationperiod and the second application period combined comprise a continuoustime period where the impedance of the tissue remains below an initiallevel of impedance in the tissue.
 8. The surgical system of claim 1,wherein the at least one energy delivery component is configured totransmit RF and ultrasonic energy.
 9. A method for transmittingelectrosurgical energy to tissue at a surgical site by a surgicalsystem, the method comprising: causing, by an energy delivery componentof a surgical system, electrosurgical energy to be applied to thetissue; measuring, by at least one sensor of the surgical system, abenchmark level of impedance of the tissue; and determining, among aplurality of power load curve algorithms, a power load curve algorithmto be applied to the energy delivery component, based on the measuredbenchmark level of impedance of the tissue; based on the determinedpower load curve algorithm: for a first application period, causing theenergy delivery component to transmit the electrosurgical energy at afirst power level, the first application period comprising a point intime where impedance of the tissue reaches a minimum impedance value;for a second application period after the first application period,causing the energy delivery component to transmit the electrosurgicalenergy, starting from a predetermined proportion of a transitionimpedance threshold level and decreasing the electrosurgical energy at asteady rate from the first power level until a second power level isreached, wherein the second power level is lower than the first powerlevel and the second application period comprises a point in time wherethe impedance of the tissue rises above the minimum impedance value; andfor a third application period after the second application period,directly after reaching the second power level, causing the energydelivery component to reduce the second power level to a third powerlevel while maintaining a constant level of the impedance of the tissueto transmit the electrosurgical energy at the third power level upon theimpedance of the tissue reaching the transition impedance thresholdlevel, the third power level lower than the second power level and thethird application period comprising a point in time where the impedanceof the tissue rises above the transition impedance threshold level. 10.The method of claim 9, wherein determining the power load curvealgorithm comprises determining whether the benchmark level of impedanceis less than a first threshold impedance value, whether the benchmarklevel of impedance is greater than the first threshold impedance valueand less than a second threshold impedance value, and whether thebenchmark level of impedance is greater than the second thresholdimpedance value.
 11. The method of claim 9, wherein the firstapplication period and the second application period combined comprise atime period where the electrosurgical energy is delivered at a higherrate and causes sealing of the tissue at the surgical site.
 12. Themethod of claim 9, wherein the third application period furthercomprises a time period where the impedance of the tissue rises to alevel such that the electrosurgical energy is delivered at a lower rateand no longer causes sealing of the tissue at the surgical site.
 13. Themethod of claim 9, wherein the benchmark level of impedance is theminimum impedance value or an initial level of impedance of the tissue.14. The method of claim 9, wherein a beginning of the third applicationperiod is based on the measured benchmark level of impedance.
 15. Themethod of claim 9, wherein the first application period and the secondapplication period combined comprise a continuous time period where theimpedance of the tissue remains below an initial level of impedance inthe tissue.
 16. The method of claim 9, wherein the energy deliverycomponent is configured to transmit RF and ultrasonic energy.
 17. Asurgical instrument comprising: a handle assembly; a shaft coupled to adistal end of the handle assembly; an end effector coupled to a distalend of the shaft and comprising at least one energy delivery componentconfigured to transmit electrosurgical energy to tissue at a surgicalsite; and a control circuit communicatively coupled to the at least oneenergy delivery component and programmed to: for a first applicationperiod, cause the at least one energy delivery component to transmit theelectrosurgical energy at a first power level, the first applicationperiod comprising a point in time where impedance of the tissue reachesa minimum impedance value; for a second application period after thefirst application period, cause the at least one energy deliverycomponent to transmit the electrosurgical energy, starting from apredetermined proportion of a transition impedance threshold level anddecreasing the electrosurgical energy at a steady rate from the firstpower level until a second power level is reached, wherein the secondpower level is lower than the first power level and the secondapplication period comprises a point in time where the impedance of thetissue rises above the minimum impedance value; and for a thirdapplication period after the second application period, directly afterreaching the second power level, cause the at least one energy deliverycomponent to reduce the second power level to a third power level whilemaintaining a constant level of the impedance of the tissue to transmitthe electrosurgical energy at the third power level upon the impedanceof the tissue reaching the transition impedance threshold level, thethird power level lower than the second power level and the thirdapplication period comprising a point in time where the impedance of thetissue rises above the transition impedance threshold level.
 18. Thesurgical instrument of claim 17, wherein the first application periodand the second application period combined comprise a time period wherethe electrosurgical energy is delivered at a higher rate and causessealing of the tissue at the surgical site.
 19. The surgical instrumentof claim 17, wherein the third application period further comprises atime period where the impedance of the tissue rises to a level such thatthe electrosurgical energy is delivered at a lower rate and no longercauses sealing of the tissue at the surgical site.
 20. The surgicalinstrument of claim 17, further comprising at least one sensorconfigured to measure an initial level of impedance in the tissue andthe minimum impedance value in the tissue.